One of the two inventors of the present invention has invented a vortex flowmeter technology that is capable of measuring vortex shedding frequencies in air flows under the standard condition as low as one meter per second and in water flows as low as five hundredths of a meter per second. Unfortunately, in many applications of the flow measurements by using the vortex flowmeters, the working environments are subjected to various types of acoustic and mechanical vibrations, which create noise overshadowing the weak vortex signals generated by fluid flows at low velocities and, consequently, limit the minimum fluid velocities measurable with a vortex flowmeter. The present invention teaches a method for enhancing the vortex detecting capability of a vortex sensor included in the vortex flowmeter that operates under noisy ambient conditions by using a plurality of parallel electronic filters operating in a multiplexing mode controlled by switching based on the frequency of the vortex generated electrical signal.